Almond N - P - K Crop Use and Variety Differences

Each year when the almonds are harvested, a significant amount of nutrients are removed from the orchard. Research by Dr.Patrick Brown  (UC Davis) and colleagues has shown that approximately 58 pounds of nitrogen, 7 pounds of phosphorous, and 51 pounds of potassium are removed for every 1000 pounds of kernals harvested. Nutrients must be either supplied by the parent soil material (as the case with phosphorous and potassium) or re-applied back to the orchard through fertilization. Furthermore, the amount of nutrients removed per pound of kernals is relatively the same for each variety; thus varieties can be fertilized to match the respective yields in order to increase nitrogen use efficiency. Young trees (less than 8 years) may need more fertilizer to maintain crop production AND vigorous growth.

For example, lets say a 12th leaf 50%-25%-25% Nonpareil, Monterey, and Sonora orchard yields 3200, 3000, and 2500 lbs/acre, respectively giving an average of 2975 kernal pounds per planted orchard acre. Within this 50%-25%-25% planting, total N-P-K usage by Nonpareil is 93, 11, 82 lbs/planted orchard acre, respectively (50% of 185,22, and 163 lbs of N-P-K that would be utilized by a fully planted acre of Nonpareil); Monterey 44, 6, and 39 lbs of N-P-K/planted orchard acre, respectively (25% of what would be used by a fully planted acre); for the Sonora 34, 5, 32 lbs of N-P-K/acre, respectively (again, 25% of what would be used by a fully planted acre). As expected, a larger amount of nutrients are needed by the tree for the higher yielding varieties. (NOTE: Applying only the amount of each nutrient used by the tree will eventually lead to deficiency due to the inefficiency of nutrient applications. This is especially true with nitrogen, which can vary significantly in its application efficiency. This was covered in an earlier blog)

In many cases growers would apply fertilizers to match the average yield of all three varieties (2975 lbs/acre). In this scenario, the lower-than-average yielding varieties would receive the same rate of nutrients as the higher-than-average yielding variety. This would lead to an excess of nutrients being applied to the lowest yielding variety, while a deficient amount of nutrients would be applied to the higher yielding varieties. Another possibility is to fertilize to match the maximal variety yield. In this case, excess nutrients would be applied to the varieties yielding less than 3200 pounds/acre.

So, why should we and how can we apply the right amount of nutrients to each of the differing varieties?

By applying different rates of nutrients to varieties, nutrient use efficiency will increase, decreasing our nutrient use (and saving money) while also reducing environmental concerns.  One way is to establish the orchard with different irrigation manifolds/systems for each variety. By doing this we could fertigate the different amounts on to each of the varieties by adjusting the duration of  fertigation. Currently this would be time consuming, but hopefully future technologies will provide some tools to help manage this type of application. Another possibility - and a bit more practical - is to apply the nutrients through a variety of application techniques. By using fertigations, broadcast, and banded applications, varied rates can be made by making multiple passes and  extra applications. In this case, the nutrients used by the lowest yielder would be the "baseline." The baseline nutrient amount would be applied to all trees, while the varieties needing more nutrients would receive extra applications to meet their needs.

I will admit that this concept may be premature. Never-the-less, with the impending regulations that will regulate the amount of nutrients applied per acre, it will become necessary to increase our application efficiency. Applying to match varietal needs will become important in order to maintain crop yields and orchard sustainability.